i) Field of the Invention
This invention relates to vesicles and a process for producing them from erythrocytes, as well as to a complex of the vesicles with a bioactive agent, a method of producing the complex, and to a method of administering a pharmacological agent, for example, a drug to a patient, and to use of the vesicles as a bioactive agent carrier and in the manufacture of a complex.
ii) Description of Prior Art
Encapsulation of bioactive compounds in natural (Ihler G. M., 1979, In: Drug Carriers in Biology and Medicine, Gregoriadis G. ed. London, Academic Press, pp. 129-153; and Ihler, 1986, In: Methods of Drug Delivery, Ihler ed., Oxford, Pergamon Press, pp 3-21) or synthetic matrixes has been extensively studied over the past decades. Advantages of such a strategy of administration are numerous. First, it provides a protection from the inactivation or degradation of molecules by the metabolism of the cell or by the immune system (see Ihler above). Secondly, it controls the kinetics of bioactive agent release, allowing the optimization of the blood concentration profile. This diminishes the deleterious effects of bioactive agents with short half-lives. While liposome technology seems very promising, the physical complex of the bioactive agent encapsulated in these artificial membranes causes several problems related to immunological reactions or to a rapid withdrawal of the complex from blood circulation. Furthermore, toxic levels of the entrapped agents in the reticuloendothelial system from the liver and the spleen are often observed with liposomes.
Resealed erythrocyte ghosts and carrier erythrocytes have been used for the encapsulation of biologically active molecules (see Ihler above). These bioactive agent carriers have been widely employed because they are naturally-occurring, biodegradable, non-immunogenic, nontoxic and nonpyrogenic and readily available in large quantities.
It has been reported that erythrosomes or erythrocyte ghosts are a good vehicle for daunorubicin (DNR) transport in the blood circulation (Gaudreault et al., 1989, Anticancer Res. 9:1201-1206; Kitao et al., 1980, Cancer Res. 40:1351-1353; DeFlora et al., 1986, Proc. Natl. Acad. Sci. U.S.A. 83:7029-7033; Zocchi et al., 1989, Proc. Natl. Acad. Sci. U.S.A. 86:2040-2044; and Tonetti et al., 1991, Am. J. Vet. Res. 52: 1630-1635) as well as for other drugs (Zimmermann et al., 1978, J. Clin. Chem. Biochem. 16:135-144; DeLoach et al., 1988, Biotechnol. Appl. Biochem. 10:359-364; and Kruse et al., 1987, Biotechnol. Appl. Biochem. 9:123-140) and for various enzymes (Thorpe et al., 1975, Pediat. Res. 9:918-923). The main advantage of such system is undoubtedly the long half-life of the erythrosomes in the circulation. The half-life of the erythrosomes in the circulation is estimated to be several days. However, recent results on the importance of cell wall flexibility involved in the phagocytosis of red blood (Lejeune et al., 1992, Biol. Cell 74:211-216) demonstrated the need for carriers able to escape rapid elimination by the liver and the spleen.